1. Field of the Invention
The present invention relates to a virtual three dimensional space sharing system in which a plurality of users geographically separated can communicate with each other, in a virtual three dimensional space created on a computer network, using a plurality of information media such as three dimensional or two dimensional computer graphics, real-time video, live sound, voice and pre-recorded sound, in a large wide-area network that co-exists with the wide-band/high-speed networks and narrow-band/low-speed networks.
2. Description of the Prior Art
FIG. 19 illustrates an example of a conventional virtual three dimensional space sharing device which is disclosed, for example, in the Japanese laid-open publication 7-288791. For the sake of simplicity, FIG. 19 illustrates a case where one virtual space sharing device accommodates three terminals.
FIG. 19 illustrates a virtual space sharing device 2010. The virtual space sharing device 2010 includes line interface units 2011, 2012 and 2013, a position information distributing unit 2014, a distance calculating unit 2015, a visual axis matching calculating unit 2016, and a video thinning rate determining unit 2017, and an inter-video thinning/distributing unit 2018.
The virtual space sharing device 2010 further includes video receiving internal buses 2019, 2023 and 2027, video transmitting internal buses 2020, 2024 and 2028, position information transmitting internal buses 2022, 2026 and 2030, a distance calculation result transferring internal bus 2031, a video thinning rate notifying internal bus 2033 and communication lines 2034, 2035 and 2036 (INS64).
The operation of this device is explained below. The virtual space sharing device 2010 transmits/receives the video and position information via INS64 lines 2034, 2035 and 2036 to/from the terminals. Initially, the data from the lines 2034, 2035 and 2036 are received in the line interface units 2011, 2012 and 2013.
The line interface units 2011, 2012 and 2013 analyze the received data. If the data are video, the video is transferred to the inter-video thinning/distributing unit 2018 via internal buses 2019, 2023 and 2027, and also to the distance calculating unit 2015 and the visual axis matching calculating unit 2016 via internal buses 2021, 2025 and 2029.
The position information distributing unit 2014 copies the position information which is received from the internal bus 2021, and transfers the copy to the line interface units 2012 and 2013 via the internal buses 2026 and 2030. The position information distributing unit 2014 also copies the position information which is received from the internal bus 2025, and transfers the copy to the line interface units 2011 and 2013 via internal buses 2022 and 2030.
Furthermore, the position information distributing unit 2014 copies the position information which is received from the internal bus 2029, and transfers the copy to the line interface units 2011 and 2012 via the internal buses 2022 and 2026.
The distance calculating unit 2015 calculates the mutual distance d from the position information received from the internal buses 2021, 2025 and 2029. By comparing the calculated distance d with the depth L of a virtual space, if 0&lt;d.ltoreq.L/4, the value 4 is given and transferred to the video thinning rate determining unit 2017 via internal bus 2031. If L/4&lt;d.ltoreq.L/2, a value 2 is given, if L/2&lt;d.ltoreq.3L/4, a value 2 is given, and if 3L/4.ltoreq.d.ltoreq.L, a value 1 is given, and these values are transferred to the video thinning rate determining unit 2017 via internal bus 2031.
The visual axis matching calculating unit 2016 calculates the cross angle .theta. between the visual axes of the users according to the position information received via internal buses 2021, 2025 and 2029. If the visual field of one user overlaps with that of another at a particular terminal, the user is assigned with a value 3, and the value 3 is transferred to the video thinning rate determining unit 2017. If the visual field does not overlap and 0&lt;.theta..ltoreq.45.degree., a value 2 is assigned, if 45.degree.&lt;.theta..ltoreq.90.degree., a value 1 is assigned, and if 90.degree.&lt;.theta..ltoreq.180.degree., a value 0 is assigned, and these values are transferred to the video thinning rate determining unit 2017.
The video thinning rate determining unit 2017 calculates a product of d and .theta. for each user. Based on the calculated product, the transmission bit rate distribution to the respective user's terminal is determined by proportional distribution so that their total amount is 64 kbit/second. The determined transmission bit rate distributions is transferred to the video thinning/distributing unit 2018 via internal bus 2033.
The video thinning/distributing unit 2018 thins the video received from the internal buses 2023 and 2027, and transmits the result to the internal bus 2020 based on the transmission bit rate distribution received from the video thinning rate determining unit 2017 via internal bus 2033. The video thinning/distributing unit 2018 does the same for the video received from 2019 and 2027, and transmits the result to the internal bus 2024, and does the same for the video received form the internal buses 2019 and 2023, and transmits the result to the internal bus 2028.
The thinning process operates so as to reduce the frame numbers per second, or to reduce the resolution, or to reduce both. The line interface units 2011, 2012 and 2013 transmit the videos received from the internal busses 2020, 2024 and 2028 to the lines 2034, 2035 and 2036, respectively.
The network connection in this virtual three dimensional space sharing device is a star type connection, which is illustrated in FIG. 20. The arrangement of FIG. 20 includes terminals 2101, a video server 2103, a public network 2104 and lines 2105. The respective terminals 2101 and the video server 2103 are all connected to the public network (INS64) via the lines 2105, and the information of a virtual three dimensional space is transmitted from the video server 2103 to the respective terminals 2101. In this context, the virtual space sharing device 2010 of FIG. 19 corresponds to the video server 2103 of FIG. 20.
As explained above, a star type connection in the user environment is a prerequisite for the conventional virtual three dimensional space sharing system. Thus, in a complex network environment where wide-band/high-speed network and low-speed narrow-band network co-exist, it has been very difficult to provide efficient services to both terminal devices connected to the wide-band/high-speed network and the narrow-band/low-speed network at the same time.
In addition, because the rendering functions which are used in the respective terminal devices are not taken into account, the information is uniformly transmitted to all of the users, even when there exists significant differences of the frame rates, number of colors and resolution between the respective terminals.
Moreover, the conventional device could not efficiently use the network bandwidth when varieties of media other than video such as computer graphics, live sound, voice and pre-recorded sound are provided.
Furthermore, the users could not control the quality of information regarding a virtual three dimensional space, even when the quality deterioration is caused by the limitations of communication bandwidth.
Still further, because the conventional device only relates the information transmission from the video server side to the user terminal device side, there is no way to prevent the congestion which might occur in the network when the number of messages increases to change the objects in the virtual space in response to the user terminal devices.